As discussed in an article to Grupp et al. entitled “A New Junction Technology for Low-Resistance Contacts and Schottky Barrier MOSFETs” from the 2005 International Workshop on Junction Technology, the authors discuss the increasing severity of the challenges for engineering the source and drain (S/D) regions of advanced CMOS devices:                “The drive to shallower junctions requires extreme technology to control the dopant depth and profile, while simultaneously limiting the resistance to acceptable values. One approach to managing short-channel integrity is ultra-thin-body fully-depleted SOI technology. However, doped S/D's in ultra-thin Si suffer from excessive sheet resistance, resulting in high resistance from the channel to the silicide contact, and high contact resistance to the silicide. One approach to improving sheet resistance is elevated S/D technology. However, this adds a penalty in gate-to-drain and gate-to-source capacitance, and the issue of doping control remains. The obvious solution is metal, or “Schottky” S/D. Yet Schottky S/D MOSFETs, especially n-channel MOSFETs, have to date been generally limited by excessive Schottky barriers between the S/D and the channel.” Grupp et al., page 1.        
To address these challenges, Grupp et al. propose an ultra-thin insulator (i.e., SiNx) between the metal and the semiconductor, which purportedly lowers the Schottky barrier and reduces the S/D resistance by a factor of 5000 in Mg contacts to moderately-doped n-type Si. The authors state that the result is a low-resistance contact that may be used for contacts to doped S/D regions, as well as to replace doped S/D regions with a metal for advanced/high-performance Schottky barrier MOSFETs.
Despite the advancements in contact technology such as disclosed in Grupp et al., further improvements in metal-to-semiconductor contacts or layers may be desirable in various applications.